<?php
// Survey database interface class as intermediate for storing data from the site to the RDF database 
require_once 'rdfConstants.php';
// Include RAP Library to write RDF files
include(RDFAPI_INCLUDE_DIR . "RDFAPI.php");

/**
 * AnswerSet is a collection of answers corresponding to a Session
 *
 */
class AnswerSet extends ResearchToolObject{
	public static $filename = 'data/results/answersets.rdf';

	public $survey;
	public $respondent;
	public $answers;

	/**
	 * Constructor for an AnswerSet object
	 * @param type $uid
	 * @param type $survey
	 * @param type $respondent
	 * @param type $answers
	 */
	public function __construct($uid=null, $survey=null, $respondent=null, $answers=null)
	{
		if(!isset($uid))
		{
			$uid = md5(uniqid(rand(), true));
		}
		$this->uid = $uid;
		$this->survey = $survey;
		$this->respondent = $respondent;
		$this->answers = $answers;
	}

	/**
	 * function evaluate()
	 * evaluates the references of survey, respondent and answers.
	 */
	public function evaluate()
	{
		if(is_string($this->survey))
		{
			$result = Survey::get(array("uid" => $this->survey));
			if(!isset($result[0]))
				return false;
			$this->survey = $result[0];
		}
		if(is_string($this->respondent))
		{
			$result = Respondent::get(array("uid" => $this->respondent));
			if(!isset($result[0]))
				return false;
			$this->respondent = $result[0];
		}
		if(!empty($this->answers) && is_string($this->answers[0]))
		{
			$newanswers = array();
			foreach($this->answers as $answer)
			{
				$result = Answer::get(array("uid" => $answer));
				if(!isset($result[0]))
					return false;
				$newanswers[] = $result[0];
			}
			$this->answers = $newanswers;
		}
		return true;
	}


	/**
	 * function save()
	 * Saves the current object into the database.
	 */
	public function save()
	{
		//If evaluation fails, some references are incorrect.
		//We shouldn't save in this case. Instead - let the user know. This function returns false if the evaluation has failed.
		//TODO: Decide how to fix invalid references graciously.
		if(!$this->evaluate()) 
			return false;
		//Ensure the required folder exists.
		if(!is_dir('data/results/'))
			mkdir('data/results/');

		$model = ResearchToolObject::load(AnswerSet::$filename);


		$resourceAnswerSet = new Resource(ANSWERSET . '/' . $this->uid);
		//Remove the old value stored with the given id
		$model->subtract($model->find($resourceAnswerSet, null, null));

		//Set the new values
		$resourceAnswerSetType = new Resource(ANSWERSET);
		$predicateRType = new Resource(RTYPE);
		$model->add(new Statement($resourceAnswerSet, $predicateRType, $resourceAnswerSetType));

		$answerSetId = new Literal($this->uid);
		$predicateId = new Resource(UID);
		$model->add(new Statement($resourceAnswerSet, $predicateId, $answerSetId));

		$surveyId = new Literal($this->survey->uid);
		$predicateSurvey = new Resource(FOR_SURVEY);
		$model->add(new Statement($resourceAnswerSet, $predicateSurvey, $surveyId));

		$respondentId = new Literal($this->respondent->uid);
		$predicateRespondent = new Resource(BY_RESPONDENT);
		$model->add(new Statement($resourceAnswerSet, $predicateRespondent, $respondentId));
		
		if(isset($this->answers))
		{
			foreach($this->answers as $answer)
			{
				$answerId = new Literal($answer->uid);
				$predicateAnswer = new Resource(GIVEN_ANSWER);
				$model->add(new Statement($resourceAnswerSet, $predicateAnswer, $answerId));
			}
		}
		$model->saveAs(AnswerSet::$filename, 'rdf');
		return true;
	}

	/**
	 * function get()
	 * @param type $arguments : An array having one ore more of the following elements:
	 * 'uid', 'survey', 'respondent', 'answers'.
	 */
	public static function get($arguments)
	{
		$model = ResearchToolObject::load(AnswerSet::$filename);

		//Build the query string
		$querystring = '
			PREFIX predicates: <' . SURVEYTOOL_PREDICATES_NAMESPACE . '>
			PREFIX resources: <' . SURVEYTOOL_RESOURCES_NAMESPACE . '>
			SELECT DISTINCT ?uid, ?for_survey, ?by_respondent
			WHERE
			{
				_answerset	predicates:resource_type	resources:answerset ;
				predicates:uid ?uid ;
				predicates:for_survey ?for_survey ;
				predicates:by_respondent ?by_respondent ;
				' . ResearchToolObject::createArguments($arguments) . '
			}';
		//Query the model
		$results = $model->sparqlQuery($querystring);
		$answerSets = array();
		if(!empty($results))
		{
			foreach($results as $result)
			{
				$survey = $result['?for_survey']->label;
				$respondent = $result['?by_respondent']->label;
				$answers = 	AnswerSet::getAnswers($model, $result['?uid']->label);
				$answerSets[] = new AnswerSet($result['?uid']->label, $survey, $respondent, $answers);
			}
		}
		return $answerSets;
	}

	/**
	 * function getAnswers()
	 * @param type $uid : the uid for which the answers should be retrieved.
	 */
	private static function getAnswers($model, $uid)
	{
		$result = $model->findRegex("[(".$uid.")]", "[(given_answer)]", null);
		$iterator = $result->getStatementIterator();
		$answers = array();
		while($iterator->hasNext())
		{
			$element = $iterator->next();
			$answers[] = $element->getLabelObject();
		}
		return $answers;
	}
}